Duplicity backs directories by producing encrypted tar-format volumes
and uploading them to a remote or local file server. Because duplicity
uses librsync, the incremental archives are space efficient and only
record the parts of files that have changed since the last backup.
Because duplicity uses GnuPG to encrypt and/or sign these archives, they
will be safe from spying and/or modification by the server.

The duplicity package also includes the rdiffdir utility. Rdiffdir is an
extension of librsync's rdiff to directories---it can be used to produce
signatures and deltas of directories as well as regular files. These
signatures and deltas are in GNU tar format.
